A fuel cell system includes fuel cells which generate electric power through an electrochemical reaction of a reactant gas (fuel gas and an oxidized gas), a reactant gas supply flow path for supplying the reactant gas to the fuel cells, and a reactant gas related exhaust flow path for exhausting the reactant gas from the fuel cells. Additionally, the provision of fuel cell shutoff valves in the reactant gas and reactant gas related exhaust flow paths has been considered.
For example, the fuel cell system described in Japanese Patent Laid-Open Publication No. 2000-3717 (Patent Document 1) supplies air through an accumulator to a shutoff valve provided in a reactant gas related exhaust flow path for exhausting reactant gas related gas from a cell stack, to a three-way changeover valve provided in a fuel gas supply flow path for supplying fuel gas to the cell stack, and to a valve provided in an oxidized gas related supply flow path for supplying air to the cell stack to switch the respective valves as pilot valves.
Further, in the fuel cell system described in Japanese Patent Laid-Open Publication No. 2005-347185 (Patent Document 2), a flow path route for supplying fuel gas to a fuel cell stack is provided with a valve which is closed by a pressure difference of the flow path in front of and behind the valve, and when a pressure difference between a first pressure between the valve and the fuel cell stack at a first instance, and a second pressure between the valve and the fuel cell stack in a second instance are less than a predetermined value, it is determined that an opening failure occurs to the valve. When it is determined that the opening failure occurs to the valve, a fuel in the fuel cell stack is consumed, so that the differential pressure is made to occur in the flow path in front of and behind the valve.
In the case of the fuel cell system described in the above-described Patent Document 1, there is a possibility that the shutoff valve provided in the reactant gas system exhaust flow path, the three-way changeover valve provided in the fuel gas supply flow path, or the valve provided in the oxidized gas related supply flow path may not function even when the pressure at the pressure value for normally driving the valves acts on the pressure chambers of the valves because the valve member peripheral portions can become frozen when used in a low temperature environment, such as in below-zero temperatures, or the valve members can be caught by fixed portions because the shafts of the valve members incline with respect to the slide portions. When the valves do not function and do not normally open, the optimal supply of gas to the cell stack and of discharge gas from the cell stack are impaired, and, in an extreme case, there is a possibility that automatic stopping of the operation of the fuel cell system could be triggered.
In contrast to this, in the case of the fuel cell system described in Document 2, a valve which is closed by the pressure difference in the flow path in front of and behind the valve is provided in the flow path route. Further, when it is determined that an opening failure occurs to the valve, the fuel in the fuel cell stack is consumed which increases the differential pressure between the flow path in front of and behind the valve. Because in such a fuel cell system it is necessary to consume the fuel in the fuel cell stack in order to open the valve when an opening failure occurs to the valve, there is a desire for further improvement from the aspect of effective use of the generated electric power of the fuel cell stack.